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  • Articles  (6)
  • 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology  (6)
  • Elsevier  (6)
  • 2015-2019
  • 2005-2009  (6)
Collection
  • Articles  (6)
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  • 1
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    Comparison between the 1994–2006 seismic and gravity data from Mt. Etna: New insight into the long-term behavior of a complex volcano (2009)
    Elsevier
    Details
    Publication Date: 2017-04-04
    Description: We investigate the relationship between changes of the gravity field and the release of the seismic energy at Mt. Etna over a 12-year period (1994-2006), during which the volcano exhibited different eruptive patterns. Over the two sub-periods when intense gravity decreases occur, centered on the upper southeastern sector of the volcano (late-1996 to mid-1999 and late-2000 to mid-2001), the strain release curve displays neat long-term accelerations, with many hypocenters clustered in the volume containing the gravity source. Various evidences suggest that, since 1994 and until the breakout of the 2001 eruption, the eastern flank of Etna remained peripheral to the lines of rise of the magma from the deep storage to the surface. Accordingly, we hypothesize that, rather than being directly associated to the migration of the magma, the joint anomalies we found image phases of higher tensile stress on the upper southeastern sector, associated to increase in the rate of microfracturing along the NNW-SSE fracture zone. Such an increase implies a local density (gravity) decrease, and an increase in the release of seismic energy, thus explaining the correlation we observe. The second period of gravity decrease/strain release increase culminated in the breakout of the 2001 flank eruption, as a pressurized deeper magma accumulation used the inferred zone of increasing microfracturing as a path to the surface. This eruption marks an important modification in the structure of Etna’s plumbing system, as also testified by the absence of post-2001 long-term gravity changes and accelerations in the strain release curve and the neat modification of the seismicity and ground deformation patterns. Thus we prove that joint microgravity and seismic studies can allow zones of the medium experiencing an increase in the rate of microfracturing to be identified months to years before a magma batch is conveyed through them to the surface, setting off a lateral eruption.
    Description: Published
    Description: 282–292
    Description: 3.6. Fisica del vulcanismo
    Description: JCR Journal
    Description: reserved
    Keywords: microgravity changes ; seismic strain release ; 04. Solid Earth::04.03. Geodesy::04.03.05. Gravity variations ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
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    Seismoacoustic measurements during the July–August 2001 eruption of Mt. Etna volcano, Italy (2005)
    Elsevier
    Details
    Publication Date: 2017-04-04
    Description: On July 18, 2001, two main eruptive vents opened on the southern flank of Mount Etna volcano (Italy) at ~2100 m and ~2550 m a.s.l., respectively. The former vent fed mild strombolian activity and lava flows, while the latter represented the main explosive vent, producing strong phreato-magmatic explosions. Explosions at this latter vent, however, shifted to a strombolian style in the following days, before switching back to phreato-magmatic activity towards the end of the eruption, which ended on August 9, 2001. On August 3, a small seismoacoustic array was deployed close to the eruptive vents. The array was composed of three stations, which recorded seismic and infrasonic waves coming from both of the eruptive vents. A further seismoacoustic station, equipped with a thermal-infrared sensor, was also installed several kilometers north of the first array. Seismic signals relating to the strombolian activity at the 2100-m vent were characterized by a strong decompression at the source. Analysis of the time delays between seismic, infrasonic and infrared event onsets also revealed that ejection velocities during explosions from both vents were subsonic. Time delays between the onset of explosive events apparent in the infrared and infrasound data indicated that the explosion source at the 2550-m vent was located 220–250 m below the crater rim. In comparison, the depth of the seismic source was estimated to be between 230 and 335 m below the rim. This converts to 120–150 and 130–235 m below the preexisting ground surface. In addition, time delays between seismic and infrasonic signals recorded for the lower (2100 m) vent also revealed a seismic source that was no more than a few tens of meters deeper than the fragmentation surface.
    Description: Published
    Description: 219-230
    Description: partially_open
    Keywords: Mt. Etna ; explosive eruptions ; arrays ; seismic ; infrasonic and thermal data ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology ; 04. Solid Earth::04.06. Seismology::04.06.10. Instruments and techniques ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring ; 04. Solid Earth::04.08. Volcanology::04.08.07. Instruments and techniques
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 520 bytes
    Format: 590708 bytes
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  • 3
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    Analysis of sustained long-period activity at Etna Volcano, Italy (2007)
    Elsevier
    Details
    Publication Date: 2017-04-04
    Description: Following the installation of a broadband network on Mt. Etna, sustained Long-Period (LP) activity was recorded accompanying a period of total quiescence and the subsequent onset of the 2004–2005 effusive episode. From about 56000 events detected by an automatic classification procedure, we analyse a subset of about 3000 signals spanning the December 17th, 2003–September 25th, 2004, time interval. LP spectra are characterised by several, unevenly-spaced narrow peaks spanning the 0.5–10 Hz frequency band. These peaks are common to all the recording sites of the network, and different from those associated with tremor signals. Throughout the analysed time interval, LP spectra and waveforms maintain significant similarity, thus indicating the involvement of a non-destructive source process that we interpret in terms of the resonance of a fluid-filled buried cavity. Polarisation analysis indicates radiation from a non-isotropic source involving large amounts of shear. Concurrently with LP signals, recordings from the summit station also depict Very-Long-Period (VLP) pulses whose rectilinear motion points to a region located beneath the summit craters at depths ranging between 800 and 1100 m beneath the surface. Based on a refined repicking of similar waveforms, we obtain robust locations for a selected subset of the most energetic LP events from probabilistic inversion of travel-times calculated for a 3D heterogenous structure. LP sources cluster in a narrow volume located beneath the summit craters, and extending to a maximum depth of ≈ 800 m beneath the surface. No causal relationships are observed between LP, VLP and tremor activities and the onset of the 2004–2005 lava effusions, thus indicating that magmatic overpressure played a limited role in triggering this eruption. These data represent the very first observation of LP and VLP activity at Etna during non-eruptive periods, and open the way to the quantitative modelling of the geometry and dynamics of the shallow plumbing system.
    Description: Published
    Description: 340-354
    Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive
    Description: JCR Journal
    Description: reserved
    Keywords: long-period seismicity ; Etna volcano ; volcano monitoring ; precursor ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 4
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    Analysis of simultaneous gravity and tremor anomalies observed during the 2002-2003 Etna eruption (2007)
    Elsevier
    Details
    Publication Date: 2017-04-04
    Description: In this paper we discuss the data collected by a large aperture array of broadband seismometers and a continuously recording gravity station during the 2002–2003 eruption of Etna volcano (Italy). Seismic signals recorded during the eruption are dominated by volcanic tremor whose energy spans the 0.5–5 Hz frequency band. On three different occasions (12 November, 19–20 November and 8–9 December 2002), we observed marked increases of the tremor amplitude (up to a factor of 4), which occurred simultaneously with gravity decreases (up to 30 μGal). The three concurrent gravity/tremor anomalies last 6 to 12 hours and terminate with rapid (up to 2 hours) changes, after which the signals return back to their original levels. Based on volcanological observations encompassing the simultaneous anomalies, we infer that the accumulation of a gas cloud at some level in the conduit plexus feeding a new eruptive vent could have acted as a joint source. This study highlights the potential of joint gravity–seismological analyses to both investigate the internal dynamic of a volcano and to improve the confidence of volcanic hazard assessment.
    Description: Published
    Description: 616-629
    Description: reserved
    Keywords: Etna ; volcanic tremor ; gravity changes ; foam layer ; 04. Solid Earth::04.03. Geodesy::04.03.04. Gravity anomalies ; 04. Solid Earth::04.03. Geodesy::04.03.05. Gravity variations ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 1036216 bytes
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  • 5
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    Seismicity associated with the 2004–2006 renewed ground uplift at Campi Flegrei Caldera, Italy (2007)
    Elsevier
    Details
    Publication Date: 2017-04-04
    Description: Following the significant ground uplift (1.8 m) of the 1982–1984 bradyseismic crisis, the recent history of Campi Flegrei volcanic complex (Italy) has been dominated by a subsidence phase. Recent geodetic data demonstrate that the subsidence has terminated, and that positive ground deformation renewed in November 2004, at a low but accelerating rate leading to about 4 cm of uplift by the end of October 2006. As in previous episodes, ground uplift has been accompanied by swarms of micro-earthquakes (M ≤ 1.4) in three distinct episodes: October 2005, October 2006 and December 2006. Hypocenters of these earthquakes are mainly located beneath the Solfatara Volcano at depths ranging between 0.5 and 4 km. Inversion of S-wave spectra indicates source radius and stress drop on the order of 30–60 m and 104–9 × 105 Pa, respectively. Fault plane solutions indicate predominantly normal mechanisms. Accompanying the October 2006 swarm, we detected intense long-period (LP) activity for about 1 week. These signals consist of weak, monochromatic oscillations whose spectra exhibit a main peak at frequency 0.8 Hz. This peak is common to all the stations of the network, and not present in the noise spectra, suggesting that it is a source effect. About 75% of the detected LPs cluster into three groups of mutually similar events. Adjustment of waveforms using cross-correlation allows for precise alignment and stacking, which enhances signal onsets and permits accurate absolute arrival picks, and thus better absolute as well as relative locations. Locations associated with the three different clusters are very similar, and appear to delineate the SE rim of the Solfatara Volcano at a depth of about 500 m. The most likely source process for the LP events involves the resonance of a fluid-filled, buried cavity. Quality factors of the resonator cluster in a narrow interval around 4, which is consistent with the vibration of a buried cavity filled with a water-vapour mixture at poor gas-volume fractions. We propose a conceptual model to interpret the temporal and spatial patterns of the observed seismicity.
    Description: Published
    Description: 14-24
    Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive
    Description: JCR Journal
    Description: reserved
    Keywords: Volcano seismology ; Long-period seismicity ; Volcano monitoring ; Caldera ; Hydrothermal system ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 6
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    Seismic tomography of Central Sao Miguel, Azores (2008)
    Elsevier
    Details
    Publication Date: 2017-04-04
    Description: We determine the three-dimensional distribution of P- and S-wave velocities for Central São Miguel Island (Azores, Portugal) by tomographic inversion of local earthquake arrival times. We use P- and S-phases from 289 earthquakes recorded by a network of 20 seismometers. The model shows good resolution in the shallowest 5–6 km, as illustrated by different resolution tests. There are several velocity anomalies, interpreted as pyroclastic deposits, intrusive bodies, geothermal fields, and the effects of tectonics. A low Vp zone marks Furnas caldera, probably evidencing volcaniclastic sediments with development of intense geothermal activity. Another low Vp zone extends in correspondence of the highly fractured area between Fogo and the north coast. Conversely, strong positive anomalies are found south of Fogo and northwest of Furnas. They are interpreted in terms of high-density deposits and remnants of a plutonic intrusion. These interpretations are supported by the distribution of Vp/Vs, and are consistent with previous geological, geochemical, and geophysical data.
    Description: Published
    Description: 8-18
    Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive
    Description: JCR Journal
    Description: reserved
    Keywords: Seismic tomography ; Volcano seismology ; Crustal structure ; Azores ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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